Corrosion resistant alloys



Unite rates 277L765 Patented Jan. 15, 1957 2,777,766 coRRosioN RESISTANT ALLOYS William 0. Binder, Niagara Falls, N. Y., assignor to UHIOI] Carbide and Carbon Corporation, a corporation of New York No Drawing. Application June 4, 1952, Serial No. 291,813

4 Claims. (Cl. 75-134) This invention relates to corrosion-resistant alloys. Media causing corrosion of metals may be classified solutions.

object of this invention to provide alloys which It is an have useful resistance to both OXldlZlHg and reducing It is also an object of the invention to provide such alloys which are hot-workable.

The invention by means of which this object is achieved comprises chromium-nickel-molybdenum-iron alloys in which the proportions of balanced with respect to one another to attain the best combination of properties. The alloys of the invention contain 18% to 25% chromium; 35% to 50% nickel; 2% to 12% molybdenum; 0.1% to of tantalum or columbium or both; up to 5% tungsten; up to 2.5% copper; the remainder iron and incidental impurities; the iron content being not less than 15%. As is customary with alloys of this general nature, the alloys may contain up to 1.5% manganese and up to 0.5% silicon. Carbon is of course present unavoidably, but should not exceed 0.25% and is preferably kept as low as possible, for example less than 0.1%.

Much experimental work has shown that chromium is the most effective element in the alloys of the invention for imparting resistance to oxidizing corrosives and that nickel and molybdenum are the most effective elements for imparting resistance to reducing corrosives.

and molybdenum against reducing corrosives, and nickel and molybdenum tending to lessen the eifectiveness of chromium against oxidizing corrosives, they are balanced in the alloys of the invention so that the effectiveness of each is retained insofar as possible. Since tungsten also works against chromium with regard to resistance to oxidizing corrosives, it is also taken into account when balancing the efiective chromium content against the nickel content. From this experimental work, the follow ing relationship was derived:

Percent Cr% (percent Mo+0.3 (percent W) 6.6 (percent Ni) The left hand side of this equation represents effective chromium. To attain the optimum resistance to both present in the alloys of the invention. Within the range Percent Cr+2(percent Mo) +V2 (percent W)+ 4(percent Ta) +2.5 (percent Cb) =6.8(percent Ni) As in the case of the first equation, for the most consistently efiective resistance, the alloys of the invention should be so balanced in composition that the left hand side of of the equation is at least equal to the right hand side.

In a properly balanced alloy the elements columbium and tantalum, in addition to improving pit resistance,

rosion resistance is required after Welding, the alloys should be annealed by heating to 1100 C. to 1150 C. followed by cooling relatively rapidly.

To provide good resistance to oxidizing media after welding and stress-relieving, about 1% of columbium or tantalum is required when the molybdenum content is If the molybdenum content is higher, say 6%, it is preferred to add 2% of these elements to the alloy. Tantalum and columbium may be present together, and although they may be present in any ratio, a 1:1 ratio is preferred for economic reasons.

For optimum resistance to pitting after welding and stress-relieving, the nickel content of the alloys should be Percent Composition; Remainder Fe and 1 5% Max. Mn and 0.5% Max. Si

Alloy No.

Results obtained in one 48-hour period.

overcome by increasing the chromium and molybdenum contents. Since the latter elements promote the decomposition of the solid solution, it is important not to increase the amount of these elements beyond that required to overcome the influence of nickel.

Copper may be present in the alloys of the invention in minor proportions as an impurity. It may be added as an alloying constituent, and relatively small proportions of copper are beneficial in increasing the resistance to corrosion of the alloys in reducing acids such as dilute hydrochloric acid and sulfuric acid in concentrations of about to 50%. Resistance to attack by hot phosphoric acid is also enhanced by the presence of copper. Although copper is beneficial in quantities up to 2.5%, larger quantities tend to lower the resistance of the alloys to pitting and contact corrosion. Therefore the alloys generally should contain not more than 2.5% copper, and a preferred range is 0.25% to 1%. In these small proportions copper may be omitted from consideration in the equations above set forth despite indications that in the alloys of this invention copper behaves like nickel and somewhat more powerfully.

Many hundreds of tests of the alloys of the invention have been made, and such tests have demonstrated that the alloys possess useful resistance to oxidizing corrosives, reducing corrosives and solutions of the type which cause pitting. For such tests samples 1 inch wide, 1% inches long and .4 inch thick were machined from A inch plate which had been rolled directly (at initial rolling temperature of 1150 C. to 1200 C.) from ingots 2 inches square. The samples were heated 30 minutes at, 1100 C.', cooled in air, descaled in a nitric acid- 2% hydrofluoric acid bath at 70 C., drilled for mounting, and polished. Before immersion in the testing so lutions, each sample was degreased and carefully measured and weighed.

Different samples prepared as described were immersed in four different media; boiling 65% nitric acid; boiling 10% sulfuric acid; aerated 10% hydrochloric acid at 70 C. and 5% ferric chloride-10% sodium chlo ride at C. The samples were suspended in the acids for three 48 hour periods being removed and weighed between periods, and results of three such 48 hour pel'iOds were averaged. in the chloride solution the samples were placed on the solution to simulate a concentration cell and to obtain an indication of the resistance of the sample to contact corrosion. The samples were kept in the chloride solution for 72 consecutive hours;

l0 Nickel stabilizes the bottom of the glass jar holding A Typical of the results obtained set forth in the following table. the acids are expressed in terms of inches per month in the table.

in such tests are those The corrosion rates in penetration Results of Corrosion Tests Average Corrosion Rate, Inch Penetration per Month Boiling 05 i Boiling 10% N itl'ic Acid Sulphuric Aerated 10% 5% FeC1 10% NaCl Hydrochloric at 25 0., 72 Hours Acid at 70 C.

No pitting. Do. Do.

It will be seen from the above table that the alloys of the invention possess useful resistance to oxidizing media, reducing media, and to chloride solutions.

That the alloys of the invention are hot-workable is demonstrated byhot-twist tests. In such tests a hotrolled sample consisting of a round bar about 22 inches long by /4 inch in diameter and having a reduced section about 8 inches long and /8 inch diameter in the center is twisted to failure. The reduced section is heated uniformly for a distance of about 3 /2 inches on each side of the center, and the bar is twisted at a constant speed of revolutions per minute. The total number of twists and the initial torque are observed. In the following table typical test results are compared with typical results obtained on conventional stainless steels. Alloy A in the table is an alloy according to this invention containing 22% chromium; 45% nickel; 6% molybdenum; 1% columbium; 1% tantalum; 1.5% manganese; 0.5% silicon; remainder iron. Alloy B is a steel containing 19% chromium; 9% nickel; 1.3% manganese; 0.4% silicon; 0.08% carbon; remainder iron and Alloy C is a steel containing 18% chromium; 15% nickel; 3% molybdenum; 1.5% manganese; 0.5%

silicon; 0.05% carbon; remainder iron.

Test Noni Alloy Temp, Torque, Twists (J. in.-lb. Before Fracture.

The data in the above table show the high order oi hotworkability which can be obtained from a Well b lanced alloy in accordance with this invention.

In general, the maximum hot-working temperature range for the alloys is 1150 to 1175 C. For optimum hot-workability the extreme limits of the broad composition range should be avoided as the alloys decrease in hot-workability as the chromium and molybdenum contents increase. The addition of tantalum benefits the hot-workability of the alloys, and it is more helpful than columbium.

The alloys of the invention may be welded by conventional methods.

7s A specific alloy according to the invention which has to 25% chromium; 35% to 50% nickel; 2% to 12? molybdenum; 0.1% to 5% in the aggregate of at lea:

chromium; 45% nickel; 6% molybdenum; 1% columbium; one metal selected from the group consisting of tantalur 1% tantalum; 1.5% maganese; 0.5% silicon; 0.05% and columbium; up to 5% tungsten; up to 2.5% coppel carbon; the remainder iron. 5 less than 0.25% carbon; the remainder iron and incidenta This 1s a continuation-in-part of my application Serial impurities, the 11'011 content being at least 15 and thl No. 100,769, filed June 22, 1949, now abandoned.

at is claimed is:

ductng-t e corrosive media, which article is composed sides thereof: of an alloy consisting of 18% to 25% chromium; 35% to 50% nickel; 2% to 12% molybdenum; 0.1% to 5% in the aggregate of atleast one metal selected from the (Percent W))=6'6(Percent NOD25 group consisting of tantalum and columbium; up to 5% Per ent Cr+2(percent Mo)+ /z(percent W)+ tungsten; up to 2.5% copper; less than 0.25% carbon; 4(percent Ta) +2.5(percent Cb)=6.8(percent Ni) the remainder iron and incidental impurities, the iron Percent Cr /3 (percent Mo+0.3

An alloy article resistant to corrosive mediaof the of said alloy being so proportioned that the left hand oxiflilmg f p the Tedllclng yp and the Plttlng iype, which article 1s composed of an alloy having substani h h i tially the following composition: 22% chromium; 45 nickel; 6% molybdenum; 1% columhium; 1% tantalum; Percent Cr (Percent 1 5% maximum manganese; 0.5% maximum silicon; less (Percent W))=6'6(Pe1'cent Nno'zfi han 0.1% carbon; the remainder iron and incidental 2. An alloy article resistant to pitting-type corrosive lmpurltles? media, which article is composed of an alloy consisting of 18% to 25% chromium; 40% to 50% nickel; 2% to 12% molybdenum; 0.1% to 5% in the aggregate of at least one metal selected from the group consisting of References Cited in the file of this patent UNITED STATES PATENTS 2,162,253 Grossman June 13, 1939 tantalum and columhlum; up to 5% tungsten; up to 1% 2,245,366 Rohn et aL June 10 1941 copper; less than 0.25 0 carbon; the remainder iron and 2,373,490 Mohling Apr. 10, 1945 incidental impurities, the iron content being at least 15% 2,403,128 Scott et a1. July 2, 4 and the individual constituents of said alloy being so 2,423,738 Thielemann July 8 1947" proportioned that the left hand side of the following 2,432,617 Franks et aL Dec. 16, 1947 equation is at least equal to the right hand side: 2,451,547 German Oct 19 1948 Percent Cr+2(percent M0)+ (pe1cent W)+ 2,504,453 Rotherham et al. Apr. 18, 1950 4(percent Ta) +2.5(percent Cb)=6.8(percent Ni) 2,553,330 Post et al. May 15, 1951 OTHER REFERENCES Iron Age, vol. 161, March 18, 1948, pages 73-75. 

1. AN ALLOY ARTICLE RESISTANT TO OXIDIZING-TYPE AND REDUCINE-TYPE CORROSIVE MEDIA, WHICH ARTICLE IS COMPOSED OF AN ALLOY CONSISTING OF 18% TO 25% CHROMIUM; 35% TO 50% NICKEL; 2% TO 12% MOLYBDENUM; 0.1% TO 5% IN THE AGGREGATE OF AT LEAST ONE METAL SELCTD FROM THE GROUP CONSISTING OF TANTALUM AND COLUMBIUM; UP TO 5% TUNGSTEN; UP TO 2.5% COPPER; LESS THAN 0.25% CARBON; THE REMAINDER IRON AND INCIDENTAL IMPURITIES, THE IRON CONTENT BEING AT LEAST 15% AND THE INDIVIDUAL CONSTITUENTS OF SAID ALLOY BEING SO PROPORTIONED THAT THE LEFT HAND SIDE OF THE FOLLOWING EQUATION IS AA LEAST EQUAL TO THE RIGHT HAND SIDE: 